1. Field of Invention
The invention relates to gas generating compositions delivering a non-toxic gas, such as nitrogen, for filling automobile restraint airbags. More particularly, the invention relates to a composition of an alkali metal azide in combination with a heavy metal sulfide and initiating oxidizers to fill the airbag with nitrogen gas.
2. Brief Description of the Related Art
The development of automobile air bags to restrain occupants upon impact in a collision is a landmark in the field of automobile occupant safety. The devices are designed to deploy when vehicles travelling at 12 mph or greater experience sudden impact. The airbag is inflated and provides a soft barrier between the occupant and the interior of the vehicle, thereby averting serious or fatal injuries to an occupant.
Typically, the airbag system fitted in an automobile consists of a sensor, which picks up the crash pulse and with the aid of a booster composition sets off a gas generating composition housed in a module. The released gas fills up a fabric bag forming a barrier between the occupant and the interior of the vehicle. The sensors used operate either on mechanical or electro-mechanical principles. In a mechanical sensor a primer is set off, whereas in an electromechanical sensor an electro-explosive device (i.e., a squibb) is set off. In turn, the squibb sets off a booster composition (Boron-KN0.sub.3) which activates the gas generating composition. The earliest gas generating compositions generated carbon-dioxide, but the state of the art is to generate nitrogen as the preferred airbag filling gas. Representative of the early nitrogen gas generating compositions for automobile airbags are those described in the U.S. Pat. No. 3,741,585 to Hendrickson et al. The state of the art gas generating compositions at the present time comprise an alkali metal azide, an oxidizer, and other additives. The gas generating compositions in use ordinarily use sodium azide as the preferred fuel. A variety of oxidizers have also been used.
Ideally, a gas generating composition for use in airbags should be a solid material, easily formed into pellets. Further, it should be non-hygroscopic and comprised of constituents which are obtainable in a relatively high degree of purity. The gas generating reaction should be easily controllable and generate the gas at the required rates and pressures. Also, the gas should produce a minimal amount of toxic gas residuals like carbon monoxide and oxides of nitrogen. The solids or slag residues formed during the reaction should be minimal and substantially retained in the combustion zone. Particles of the solid residues should be capable of being arrested in the filter system of the device. Most importantly, the slag residues should be non-toxic and generated in minimal amounts for ultimate disposal.
The gas-generating reaction should further be capable of being modified for different particular applications by either change of the physical parameters of the constituents or by use of suitable additives.